The trifluoromethylthiophenium derivative salt of the present invention has not been known. As the conventional technique about a trifluoromethylating agent, 4-chlorophenyl-2′,4′-dimethylphenyl(trifluoromethyl)sulfonium hexafluoroantimonate (Non-Patent Literature 1), (trifluoromethyl)dibenzonium salts (Patent Literatures 1 and 2), and the like have been known.